Resilient volume-enclosing member



June 8, 1965 F. s. KELLY ETAL RESILIENT VOLUME-ENCLOSING MEMBER Filed March 4, 1963 FIG.

INVENTORS FREDERICK G. KELLY S HOLOWACHUK ATTORNEY MO BY United States Patent Filed Mar. 4, 1963, Ser. No. 262,725 12 Claims. (Cl. 92-47) This invention relates to a resilient volume-enclosing member, and more precisely to a metallic volume-enclosing member to withstand deforming forces. A nonlimitative example of such a member is a metallic bellows, in terms of which the invention is herein disclosed. (The term metal and its derivatives are used herein to embrace alloys as well as individual pure metals.)

For a large number of their functions such members are required to be leakproof in very high degree (a typical requirement being for a gas-tightness so great that with a pressure difference of only one atmosphere existing across the wall of the member, less than 1 cc. of gas would pass through the wall in 32 years), and it is an important object of the invention to provide a leakproof but economical such member. The provision of a leakproof member becomes the more difficult, the thinner be the member wall, and in practice this has limited the thinness of wall which could be achieved; it is an important object of the invention to make possible the achievement of materially thinner-walled members than have hitherto been practical.

A general method very useful for the production of such members is the formation of the member wall by electrodeposition on a suitably formed mandrel, which after the wall is formed is dissolved away or otherwise removed from the wall. The art of electroplating currently permits the creation in this manner of a wall, typically of almost-pure nickel, which has excellent resilience or spring quality, high elastic limit, long endurance in the face of repeated deformations, toughness, ductility, and surface brightness and resistance to corrosion. It has, however, been difficult, especially with very thin-Walled members, to avoid random defects in the form of minute transverse holes or faults through the wall which result in gas-perviousness or so-called porosity of the member.

In practice such faults, even with relatively thick-walled members (e.g., of many thousandths of an inch wall thickness) and although there has been taken every care not inconsistent with the qualities just mentioned, may force the rejection of as much as of the product; with wall thicknesses of the order of .001" the rate of required rejection may rise to as high as about 85%. It is an important object of the invention to provide for such a method improvements which drastically reduce such rejection rates.

According to one aspect of the invention the member is formed with a wall comprising inner and outer layers each of metal which has a substantial unit elastic limit (i.e., elastic limit per unit of cross section) but is prone in such layers to transverse faults, and an intervening layer of metal which has a lower unit elastic limit but is relatively substantially less prone to transverse faults, the successive layers being intimately adherent to each other. The intervening layer may be substantially thinner than either of the inner and outer layers and its metal may even in such a thinner layer be substantially less prone to such faults; it may, although it is not always required to be, itself a gas-impervious layer. Each of the inner and outer layers may desirably be of almostpure nickel. The intervening layer may typically, although not in the broadest aspect limitatively, be of Patented June 8, 1965 metal softer than that of either of the inner and outer layers. The thickness of the intervening layer may be a small fraction of the aggregate thickness of the three layers, with the result that the abovementioned desirable qualities of the member are little influenced by the intervening layer. The ratio of the thickness of either of the inner and outer layers to that of the other may be limited to at most of the order of 2.5 and may more ideally approach unity, with the result that the intervening layer will lie at a section within the wall where the stress attendant upon deformation of the member is small or essentially zero.

Another aspect of the invention relates to the making of the member by the electrodeposition of its well on a mandrel. Out of a first bath there is electroplated a metallic deposit prone to transverse faults but of substantial unit elastic limit; out of a second bath different from the first there is electroplated an intimately adherent metallic deposit substantially less prone to transverse faults but of lower unit elastic limit; out of a third bath different from the second there is electroplated an intimately adherent metallic deposit which relative to the second is substantially more prone to transverse faults but is of higher unit elastic limit; and from the thusdeposited wall the mandrel is removed. The second deposit may be substantially smaller than either of the first andv third; it may, although it is not always required to be, itself a gas-impervious deposit. The first and third baths may be at least substantially the same. The second bath may be a strike-type or a levelling-type bath; typically the first and third may be of some other type or types.

Various objects of the invention have been stated above and others made apparent in the foregoing brief description of the invention. Allied and still other objects will appear from the following detailed description and the appended claims.

In the detailed description of the invention reference is had to the accompanying drawing, in which:

FIGURE 1 is a side view of a typical bellows in which the invention may be embodied, with certain portions shown in section;

FIGURE 2 is a tremendously enlarged showing of such a section of the bellows as is indicated at 2 in FIG- URE 1; and

FIGURE 3 is a view similar to FIGURE 2 but illustrating a dimensional modification.

FIGURE 1 shows a typical volume-enclosing member in the form of a metallic bellows 10. By way of example this has been illustrated as having at its right a closed end 11, and at its left an end which is open but which, subsequent to the formation of the bellows 1t) proper, has been fitted about and hermetically sealed (as by soldering) to the periphery of a metallic closure member 9. (Such fitting may call for spinning of the end portion of the bellows to a properly tailored diametercapability of being spun, as well as ability to resist shocks resulting from handling and minor abuse, being considerations rendering ductility of the bellows material usually important.) The closure member 9 might typically be provided with a neck 8 which is threaded for insertion into the apparatus (not shown) with which the bellows is to be used and which has an axial bore 7 "to provide for fluid communication between the interior of the bellows and the interior of that apparatus. A typical function of the bellows may be to elongate and contract in the direction of its axis, thereby displacing its closed end 11 rightwardly and leftwardly, under the influence of variations of the pressure of the fluid therewithin.

The wall of the bellows It may be of metal of essentially uniform thickness throughout. In FIGURE 1 that wall appears in cross section in the region of the upper portion of the closure member 9 and at another arbitrarily chosen region 2; in both those regions, by reason of limitations imposed by the mechanics of illustration, the thickness of the wall is shown as relatively much larger than it may be in practice, and the wall appears with no indication of any laminar nature and without sectional hatching.

FIGURE 2 illustrates the wall cross section at the arbitrarily chosen region 2, in a tremendously enlarged scale which overcomes the limitations just referred to; it also includes a fractional showing of a mandrel M on which the bellows may have been initially formed and which is hereinafter referred to. In FIGURE 2 it will be seen that the bellows wall comprises first an inner layer 21 which may for example be of almost-pure nickel and which has the desirable characteristics introductorily mentioned (excellent spring quality, high unit elastic limit, long endurance, toughness, ductility, and surface brightness and resistance to corrosion) but which is prone to random faults such as referred to above; secondly, an intervening layer 22 of metal which has a lower unit elastic limit but is relatively less prone to transverse faults and which is intimately adherent to the first layer; and thirdly an outer layer 23 which like the layer 21 has the desirable characteristics introductorily mentioned but is prone to random transverse faults, which may for example also be of almost-pure nickel, and which is intimately adherent to the layer 22. Preferably the intervening layer 22 is substantially thinner than either of the layers 21 and 2.3, and the metal of which it consists is even in such a thinner layer substantially less prone to transverse faults. Desirably, but (forreasons hereinafter set forth) not mandatorily, the intervening layer 22 may be itself a gas-impervious layer.

The intervening layer 22 may be of a metal softer than, and at least predominately different constituently from, that of either of the inner and outer layers 21 and 23. Among metals of which it may then consist there may be mentioned by way of example copper, silver, gold and platinum. Alternatively, and as hereinafter more detailedly dealt with, it and the other two layers may be predominately of the same metalbut subject to the limitations of the preceding paragraph as to relative unit elastic limit and relative proneness to transverse faults.

As shown in FIGURE 2, the thickness of the intervening layer 22 is substantially less than that of either of the inner and outer layers 21 and 23, and is preferably a small fraction-for example between and /5,

even though those characteristics or many of them be lacking from the intervening layer itself.

As shown in FIGURE 2, the inner and outer layers 21 and 23 are of essentially the same thickness, so that the ratio between their thicknesses is essentially unity. This proportioning places the transverse center of the intervening layer 22 at the transverse center of the wall, Where the stresses incident to the operative or other bending of the wall (which appear as compression at one surface of the wall and as tension at the opposite surface) are zero. Even taking into account the finite thickness of the intervening layer, the maximum stress appearing at any point within it remains a small fraction of the stresses at the Wall surfaces; accordingly the mechanical strength, and in particular the unit elastic other mechanical characteristics.

41 of such mechanically weaker materials as have been typically mentioned above (whose unit elastic limits are in general distinctly minor fractions of that of the material, almost-pure nickel, typically used for the inner and outer layers).

In practice with typical materials it has been found that it is not necessary to maintain by any means full equality between the thicknesses of'the inner and outer layers 21 and 23, and that one of those thicknesses may be permitted to be as high as about 2.5 times the other without appreciable prejudice to the endurance or other qualities of the bellows. Thus the alternative FIGURE 3 illustrates the cross section of the bellows'wall in which the thickness of one of those layers, by way of example that of the outer layer (therein designated as 23'), has been made about 2.5 times that of the other layer (i.e. the inner layer, therein designated as 21).

In the making of a bellows such as above described a metallic deposit (e.g. the inner layer) may first be electroplated on the suitably formed mandrel (e.g. M, fractionally seen in FIGURE 2); this deposit may be electroplated out of a first bath and with a technique best adapted to achieve the various characteristics (spring quality, high unit elastic limit, etc. etc.) introductorily mentioned, even though such bath and technique increase the proneness of that deposit to transverse faults. Next an intimately adherent metallic deposit (e.g. the intervening'layer) may be electroplated out of a second bath different from the first; this step is more detailedly discussed below. Next an intimately adherent metallic deposit (e.g. the outer layer) may be electroplated out of a third bathrand with a technique adapted to achieve similar ends to the first bath and technique (as well as the intimate adherence). Any of a variety of baths (though usually not a strikeor a levellingtype bath) may be used for the first andthird deposits in accordance with the technology appropriate to the formation by electrodeposition of non-laminar bellows;

conveniently though not imperatively the first and third baths may be at least substantially the same. Finally the mandrel may be dissolved or otherwise removed from the thus-deposited wall in accordance with known practice. l l inl Attention may now be directed to the electroplating of the second deposit. This is called upon to minimize transverse faults in the plated metal as well as to provide an intimate adherence of that metal to the metal previously deposited, and is carried out in a bath and with a technique primarily adapted to' achieve those results at an attendant sacrifice in unit elastic limit, if not also As non-limitative examples of an appropriate bath there may be mentioned one either of the strike type or of the levelling type. When copper is the metal of which the second deposit is electroplated the strike-type bath has in practice proven easier to employ; on the other hand with many metals, in particular including the silver, gold and platinum specifically mentioned above, either of those types may be employed.

In some of its aspects the invention is not limited to the second deposit (or intervening layer) being of a metal predominately different constituently from that or those of the first and third deposits (or inner and outer layers). Thus it has been found that, with almost-pure nickel forming the inner and outer deposits, nickel may be used for the intervening deposit if it be electroplated out of a levelling-type bath, and that there may still be achieved a very satisfactory intervening layer and an output of bellows exhibiting a very low rate of required rejection for leakage. In this case the contrast of unit elastic limit between the second deposit on the one hand and the first and third deposits on the other hand has not been as great as typically indicated above, but has still been appreciable.

An advantage of the dissimilarity of the metal of the second deposit from the metal or metals of the first and third deposits, or of the dissimilarity of the bath out of which the second deposit is electroplated from that or those out of which the first and third deposits are electroplated, or of both those dissimilarities jointly, is found to be a far greater assurance of the creation of a leakproof wall. The metal of the second deposit may itself be one (such as the copper, silver, gold or platinum exemplarily mentioned above) itself well adapted to electrodeposition with a minimum of transverse faults, and the bath out of which it is electroplated may be one (such as the strike-or levelling-type baths mentioned above) well calculated to that end. It appears, however, that there is a further and independent action strongly contributing to the improved results. This we believe is due to the fact that in being electroplated over one deposit, a succeeding deposit of a dissimilar metal or out of a different-type bath or both will not reproduce the same metallographic granular structure; in other words, faults in the one deposit will not be perpetuated in the succeeding one-even though in the succeeding one there might be developed an independent fault at some new point which is unaligned with any fault in the prior one and is therefore eifectively closed by that prior one.

With the practice of the invention in the manufacture of bellows having wall thicknesses of the order of one to several thousandths of an inch, the intervening layer being of a metal different from that of either of the inner and outer layers, there have been achieved in production reductions of the rates of rejection for leakage to the order of of the corresponding rates for bellows of the usual non-laminar-wall variety but otherwise similar-an altogether startling reduction indeed. Large reductions have also been achieved, as indicated above, with the intervening layer predominately similar constituently to the inner and outer layers but electroplated out of a different-type bath.

While we have disclosed our invention in terms of particular embodiments and operational procedures, we intend thereby no unnecessary limitations. Modifications in many respects will be suggested 'by our disclosure to those skilled in the art, and such modifications will not necessarily constitute departures from the spirit of the invention or from its scope, which we undertake to define in the following claims.

We claim:

1. A volume-enclosing member to withstand deforming forces having a wall, of thickness of the order of one to several thousandths of an inch, comprising inner lower unit elastic limit but is relatively substantially less prone to transverse faults, said inner and intervening layers and said intervening and outer layers being intimately adherent to each other.

2. The subject matter claimed in claim 1 wherein said intervening layer is substantially thinner than either of said inner and outer layers and wherein said metal of which it consists is even in such a thinner layer substantially less proneto transverse faults.

3. The subject matter claimed in claim 1 wherein said intervening layer is itself a gas-impervious layer,

4. The subject matter claimed in claim 1 wherein the metal of which said inner layer consists, and the metal of which said outer layer consists, is almost-pure nickel.

5. The subject matter claimed in claim 1 wherein said metal of which said intervening layer consists is a metal softer than that of which either of said inner and outer layers consists.

6. The subject matter claimed in claim 1 wherein said metal of which said intervening layer consists is a metal at least predominately different constituently from that of which either of said inner and outer layers consists.

7. The subject matter claimed in claim 1 wherein the metals of which said inner and outer and intervening layer-s respectively consist are predominately the same constituently.

8. The subject matter claimed in claim 1 wherein the thickness of said intervening layer is a small fraction of the aggregate thickness of said three layers.

9. The subject matter claimed in claim 1 wherein the ratio of the thickness of either of said inner and outer layers to that of the other is at most about 2.5.

10. The subject matter claimed in claim 8 wherein the ratio of the thickness of either of said inner and outer layers to that of the other is at most about 2.5.

11. The subject matter claimed in claim 1 wherein the thicknesses of said inner and outer layers are substantially the same.

12. The subject matter claimed in claim 1 wherein said member is a bellows.

References Cited by the Examiner UNITED STATES PATENTS 1,368,253 2/21 Fulton 92-47 1,825,652 10/31 Buell 92-47 1,905,583 4/33 Giesler 92-47 2,137,806 11/38 Paige 204-9 2,889,258 6/59 Fialkotf 204-9 3,061,525 10/62 Grazen 204-9 RICHARD B. WILKINSON, Primary Examiner.

KARL J. ALBRECHT, Examiner. 

1. A VOLUME-ENCLOSING MEMBER TO WITHSTAND DEFORMING FORCES HAVING A WALL, OF THICKNESS OF THE ORDER OF ONE TO SEVERAL THOUSANDTHS OF AN INCH, COMPRISING INNER AND OUTER LAYERS EACH OF METAL WHICH HAS A SUBSTANTIAL UNIT ELASTIC LIMIT BUT IS PRONE IN SUCH LAYERS TO TRANSVERSE FAULTS, AND AN INTERVENING LAYER OF METAL WHICH HAS A LOWER UNIT ELASTIC LIMIT BUT IS RELATIVELY SUBSTANTIALLY LESS PRONE TO TRANSVERSE FAULTS, SAID INNER AND INTERVENING LAYERS AND SAID INTERVENING AND OUTER LAYERS BEING INTIMATELY ADHERENT TO EACH OTHER. 